The present invention relates to techniques of determining the walking state of a user and assisting the walking motion of the user.
Recently various walking assistance apparatuses have been proposed, which are of a lower-limb mounted type and are configured to assist the walking of persons who cannot perform walking motions well or have difficulty in walking for a long time because of their weakened or declined muscle strength in the lower limbs. Apparatuses of this type include a motor to give a torque to a knee joint or the like, and a detector configured to detect the walking state of a walker for suitable controlling to give the torque. The walking state of a walker is determined using a swing phase and a stance phase of the legs during walking or walking upstairs/downstairs. Therefore the detector typically includes a pressure sensor of a sole-attached type or a gravity sensor of a waist-mounted type, by which the timing when the legs come into contact with the ground (hereinafter called grounding timing) can be detected, and these phases of the legs are determined based on the grounding timing (see Patent Literatures 1 to 7, for example). A walking analysis apparatus also is proposed, which is configured to calculate the time when the leg is left from the ground and the time when the leg is grounded of a walker who is wearing an acceleration sensor and an angular velocity sensor on the leg. The analysis apparatus is configured to perform the calculations based on the absolute values of the acceleration that are detected, and set the timing of a maximum value in the first half of the detected data for each step as the time of leaving from the ground and set the timing of a maximum value in the latter half thereof as the grounding time (Patent Literature 8).
Non-Patent Literature 1 proposes a variable stiffness mechanism that is small and light-weight. The variable stiffness mechanism includes two frames coupled via a rotating member, a ball screw mechanism, a linear spring, and a motor. The linear spring is expandable between the two frames, and the elasticity of the linear spring can be changed using the ball screw mechanism, so that the linear spring has maximum elasticity energy when the stiffness of the mechanism is the maximum.